1. Field of the Invention:
This invention relates to a hydraulic accumulator and more particularly to hydraulic accumulators used for controlling the oil pressure in automatic transmissions for vehicles.
2. Statement of Prior Art:
Conventional automatic transmissions for automobiles generally include a hydraulic torque converter and a transmission gear mechanism which has a plurality of friction devices such as clutches and brakes for providing a plurality of different driving stages when the friction devices are selectively actuated. A hydraulic accumulator is provided in a hydraulic pressure line connected to each friction device.
One of the conventional hydraulic accumulators is shown in FIG. 2, wherein a piston 2 is slidably disposed in a hollow valve body 1. The piston 2 divides an interior space of the valve body 1 into two chambers, namely, first and second chambers 3, 4. The line pressure is supplied into the two chambers 3, 4 via passages 5, 7, respectively. The numeral 6 designates an orifice provided in the passage 5 leading to a manual valve. Air chamber 8 is provided in the valve body 1 and is always exposed to the atmospheric pressure via port 9. The passage 7 is normally connected to an oil pump or a primary regulator valve.
The valve body 1 has a large diameter cylinder portion 10 and a small diameter cylinder portion 11. The piston 2 is slidable between the two cylinder portions 10, 11. A spring 12 is disposed in the space of the valve body 1 to always bias the piston 2 toward the first chamber 3.
The accumulator provides the hydraulic pressure level in response to position of the manual valve due to the pressure differentials between the first and second chambers 3, 4 and the biasing force of spring 12 towards the piston 2. This conventional accumulator shown in FIG. 2 has the two different diameter cylinder portions 10, 11 as a part of valve body 1. Accordingly, if an adjustment is needed to change the effective area of the piston 2 in order to balance the pressures in the two chambers 3, 4, the valve body 1 has to be altered to change the diameters of the two cylindrical portions 10, 11.